The present invention relates to a SEM-type defect-reviewing apparatus that uses a detection system of a scanning electron microscope (SEM) to automatically acquire high-resolution images of any semiconductor wafer surface defects detected by an inspection apparatus during manufacturing processes for semiconductor products. The invention also relates to a method for reviewing defects using the SEM-type defect-reviewing apparatus.
To achieve early ramp-up of high yield manufacturing of large-scale integrated circuits and stable operation of their manufacturing process equipment, information on the occurrence of the defects detected by visual inspection apparatus, must be analyzed rapidly and utilized for defect route cause analysis. Reviewing apparatuses that automatically acquire high-resolution images of the inspection apparatus-detected defects in order to analyze obtained defect information are broadly divided into a type having an optical detection system, and a type having a detection system based on a scanning electron microscope (SEM). Compared with the optical type of reviewing apparatus, the SEM type of reviewing apparatus can obtain detailed defect images. For this reason, adoption of the SEM type of reviewing apparatus capable of obtaining high-resolution images is increasing with finer wiring patterns on semiconductor wafers. However, since SEM images require a longer acquisition time than optical images, the SEM type of reviewing apparatus has the problem that its throughput (hourly defect detection capability) is low, compared with that of the optical type of reviewing apparatus.
Known conventional techniques relating to such a SEM-type reviewing apparatus are disclosed in JP-A Nos. 2002-310962 (Patent Document 1), 2000-67243 (Patent Document 2), 2003-98114 (Patent Document 3), 2000-30652 (Patent Document 4), and 2002-323458 (Patent Document 5).
JP-A-2002-310962 describes an image acquisition apparatus that uses a SEM to automatically form and acquire images of any plural surface defect sections of a semiconductor wafer. This image acquisition apparatus has a scheduling unit for determining a defect-imaging sequence and a moving speed of a stage from a positional relationship between the defective sections on the wafer, and a control unit for feeding back to the quantity of beam deflection a moving distance of the stage. The scheduling unit and the control unit make it possible to form and acquire the images of the plural defective sections while moving the stage along an ideal route.
Also, JP-A-2000-67243 describes an automatic defect information acquisition method that uses a SEM. In this defect information acquisition method, a user can efficiently detect defects by assigning pattern information on an object to be inspected, since there is no need, for example, to move a field of view of the SEM to a reference point when inspecting a non-patterned or cyclically patterned region.
JP-A-2003-98114 describes a method for inspecting and reviewing defects using a SEM. This method includes splitting a defect image into regions of a grid format, then executing pattern matching (or the like) to evaluate whether a split image region to be inspected is similar to other split image regions, and if the evaluated region has no similarity to any other regions, identifying defect positions in that region because of the defects being regarded as included therein.
JP-A-2000-30652 describes a method for reviewing a sample using a SEM. In this reviewing method, information on defects which have been detected on the sample by an inspection apparatus is first used to image the sample and obtain a reference image not including the detected defects. Next after the information relating to the detected defects has been used to image the sample and obtain a defect image including the detected defects, the reference image and the defect image are compared and the defects within the defect image are detected. Additionally, an enlarged image of the detected defects is obtained by imaging part of a region in which the detected defects have been imaged above, then a background region is erased from the enlarged image, and the resulting image without the background region is displayed.
JP-A-2002-323458 describes a SEM-type apparatus for reviewing defects. In this apparatus, during acquisition of approximate defect position coordinates obtained during inspection with an inspection apparatus, whether the defect occurred in a cell section, a non-cell section, a section with dense patterns, or other sections, is first judged using layout data. Next, an image detection mode (a mode for determining whether a reference image is to be detected) and inspection parameters including an imaging magnification are set up according to particular judgment results, and management standards relating to criticality are established.
As outlined above, a cell comparison scheme and a die comparison scheme are used as the methods of acquiring defect images based on SEM images. The cell comparison scheme, compared with the die comparison scheme, is high in throughput, but is limited in the number of applicable semiconductor wafer types, whereas the die comparison scheme, compared with the cell comparison scheme, is low in throughput, but is applicable to almost all types of semiconductor wafers. Regions to which the cell comparison scheme can be applied, and regions to which the cell comparison cannot be applied are usually present in mixed form in a semiconductor wafer region to be reviewed, so it is difficult to improve throughput by adopting only the cell comparison scheme. To perform defect detection operations and detailed analyses while maintaining optimal throughput for semiconductor wafers, therefore, both the cell comparison scheme and die comparison scheme that are review sequences must be selected for each semiconductor wafer inspected or for each defect inspected.
However, none of the above five Patent Documents (1 to 5) has paid sufficient consideration to the fact that a review sequence suited to each semiconductor wafer and defect to be analyzed can be automatically selected using defect detection results obtained at least in the cell comparison scheme.